A Digital Subscriber Line (DSL) connection is a connection that allows for the provision of digital communication over an existing copper subscriber line. DSL is a collective term to cover a number of versions of DSL technology, including ADSL (“Asymmetric” DSL), SDSL (“Symmetric” DSL), ADSL2+(a technique that extends the capability of basic ADSL by doubling the number of downstream channels), VDSL (Very-high-bit-rate DSL), VDSL2 (an improved version of VDSL), and others, such as “G.fast”.
In general, a DSL connection comprises a copper subscriber line (strictly, a twisted pair formed from a copper loop) extending between two DSL modems. A “customer-side” DSL modem (or “user modem”) is typically located at the customer's premises, while an “operator-side” modem may be located at the local exchange (known as the ‘central office’ (CO) in US terminology), in a street cabinet, or at a drop point or distribution point (DP).
Typically, the local exchange, street cabinet, drop point or distribution point includes a DSL Access Multiplexer (DSLAM), which is a form of aggregation transceiver device comprising several DSL modems, one for each subscriber line served by the DSLAM. The DSLAM serves as the interface between copper DSL connections from customers' premises and the (generally faster) optical fibre connections of the Core Network. It is generally also connected to a network management system.
A DSL connection between a DSLAM and a user modem may simply be operated at a fixed, pre-agreed rate, but in general, broadband communication providers offer their customers a rate-adaptive broadband service, according to which the connection is set up at or near the highest rate which the line can support at the time of set-up, then varied in response to indications that the current rate can or should be increased or decreased. As such, lines generally tend to be operating at or near the limit of what is achievable, leading to a risk that their rates may be such that they become unstable. This can lead to excessive errors and even drop-outs where the connection is lost completely and needs to be completely re-established (with a lengthy initial handshake period being repeated each time, referred to as a “sync”, a “re-synch” or a “re-train”).
Dynamic Line Management (DLM) is a technique for monitoring the behaviour of DSL lines and dynamically modifying certain parameters in response to the observed behaviour. In overview, it generally involves assessing at least the stability of a line then adjusting parameters which can affect the likelihood of re-synchs occurring (for example the depth of interleaving, the amount of redundancy built into the encoding used, etc.) to try to find and maintain an appropriate balance between the line-rate and a desired level of stability. Typically this is done by selecting from a number of different DLM “profiles” having various different sets of values for the parameters likely to have an impact on the stability or otherwise of DSL connections and moving a particular connection between profiles until one is found which provides an acceptable balance between rate and stability. Profiles are applied at the DSLAM.
A single profile normally contains a complete set of all the configuration parameters and values required for a line. Many hundreds of different profiles may be available to a DLM system of which only one is applied to each line at each time. Often a degree of freedom that is added to DLM control increases the dimension of the profile space and hence greatly increases the number of profiles defined and used.
Broadband forum recommendation TR-252, Issue 3 provides for a vector of profiles (VoP), which is a set of N independent profiles, each profile containing a unique set of DSL modem configuration parameters and the value of each vector index referencing specific values of the parameters. Using a vector of profiles can significantly reduce the number of profiles required to manage a network.
Typically, profiles may be thought of as ranging between “more aggressive” and “less aggressive”, where more aggressive profiles tend to provide better services to users in terms of higher bit rates and lower latencies, but are more likely to result in lines being unstable, whereas less aggressive profiles tend to offer lower bit rates and/or latencies but greater stabilities. While higher rates and better stability are both desirable characteristics, an appropriate trade-off between them may depend on factors such as current and previous conditions, the type(s) and/or preference(s) of users of devices using networked devices served by the lines, and the networked applications they are currently using.
It is thus desirable that the profile and/or individual parameters applied in respect of a particular line can be adjusted on an ongoing basis in response to factors such as (potentially changing) user preferences and current or past usage as well as the monitored performance of the line.
Generally, in relation to DSL technology, it is well-known that speed and performance drop off markedly with increasing line length. In urban areas, this problem is generally being circumvented by bringing the fibre network and DSLAMs closer to customer premises (i.e. to the cabinet, to the drop-point, or to the premises itself), thereby shortening (or replacing) the part served by copper lines. In more rural areas, this may not be economically-justifiable. Instead, it is known for devices known as “Regenerators” to be used for customers in such rural areas whose premises are a large distance from the nearest DSLAM.
A DSL regenerator is a device that can be incorporated into a DSL connection between the DSLAM and the customer's modem to improve the performance or reach of the DSL service without needing to move the DSLAM and fibre backhaul closer to the customer premises. A regenerator generally contains a CPE chipset (including a modem) and a DSLAM chipset (also including a modem), and an Ethernet bridge between the two chipsets to transfer data between the respective links, effectively making the regenerator transparent (in both directions) to user data. A regenerator demodulates the received signal from either side to a binary signal before re-modulating the binary signal back into a transmission frequency for onward transmission, so theoretically there is no limit to the number of regenerators that can be included on a line (unlike amplifiers, which instead increase the signal level of analogue transmission signals).
Regenerators effectively split existing longer DSL connections into two or more shorter DSL links or segments, each link or segment being a twisted copper pair or “loop” capable of providing the improved speed and performance that a shorter link can provide. Each segment is then effectively an independent DSL circuit, and thereby has the normal potential data-collection and management requirements of a DSL circuit. As will be appreciated, however, for an operator to perform data-collection and management in respect of a DSL circuit, the operator needs suitable communication channels to/from the circuit and/or to devices linked to it, and in the case where a DSL connection from an operator-side DSLAM (in an exchange, for example) to a customer modem is split using a simple regenerator, the operator will generally only have direct communication with the segment from the operator-side DSLAM to the regenerator.
For a normal connection comprising a single DSL circuit, the operator generally collects DSL performance data, analyses it and applies a profile to modify the circuit operation and maintain a desired performance. The performance data and profile configuration for VDSL2 is defined in the standard G.993.2. There is normally a DLM system in the operator's Operational Support System (OSS) that processes the data and chooses appropriate profiles for each line under its control.
The functionality of a complete DLM system and of an OSS in general will not be described in detail here—DLM algorithms for managing stability and/or for balancing speed against stability are well known—and they are not shown in full in FIG. 1 (discussed below). Instead, the functionality of the OSS and of a DLM system insofar as it affects the DSL connection between the exchange DSLAM 12 and the CPE 18 is represented by OSS 14 and DLM Engine 16. Generally, however, DLM systems analyse performance data from DSL lines connected to a DSLAM under their control and select suitable profiles to be applied in respect of those lines in order to trade stability and performance, as indicated earlier.
Briefly, a typical DLM process may involve the following steps being performed in respect of each line:                1. Data is collected from the line in respect of short periods (15 minute periods, for example).        2. The data is aggregated over a longer period (a day, for example), with performance issues such as the number or rate of errors and/or retrains in the longer period, the minimum and/or maximum rate in the longer period, for example, being monitored.        3. The performance of the line is categorised with reference to predetermined performance thresholds (relating to errors, rates, latency and/or retrains, for example).        4. A DLM algorithm is run to determine whether (and if so, how) to change the profile for the line. If the number of errors is above an “error” threshold, error protection may be enabled, for example, or a line-rate cap may be reduced.        5. If applicable, the relevant DSLAM for the line is instructed to apply the newly-determined profile to the line in the network, such that transmissions over the line are made in accordance therewith.        
Of the above steps, some or all may be performed by a functional module referred to as a DLM engine. Steps 3 and 4 in particular are the key DLM processing steps.
DLM algorithms may take into account user settings such as configuration parameters or targets selected by users and/or by communication providers (CPs), as well as performance data. These user settings may indicate whether the DLM processing should prioritise speed, stability or other issues, and may be set differently for different particular users or different categories or users, possibly based on preferences specified by the users themselves, possibly based on observations by CPs of the type of networked applications the users habitually use, or otherwise.
FIG. 1 illustrates the principal functional modules involved in the operation of a standard DSL regenerator being used on a DSL connection located between a network operator's DSLAM (which, in the case of an ADSL connection, would be located in the exchange) and Customer-Premises Equipment (CPE) at the boundary of a user's local network.
In FIG. 1, a regenerator 10 is used on a DSL connection between a modem in a DSLAM 12 in an exchange and a modem in the CPE 18 via which a customer's networked user devices may be connected, splitting the connection into two links L1 and L2. Link L1 is connected to the regenerator 10 via a CPE chipset 102 which (from the point of view of the exchange DSLAM 12) mirrors the functionality of the CPE modem 18. Link L2 is connected to the regenerator 10 via a DSLAM chipset 106 which (from the point of view of the CPE modem 18) mirrors the functionality of the exchange DSLAM 12. In each case, the modems on the customer's DSL connection are shown as “M”. An Ethernet bridge 104 carries data received via one link (the data having been demodulated by the modem in one chipset) to the other chipset at which it is re-modulated for onward transmission over the other link, such that the two links effectively convey user data along the whole of the customer's DSL connection (symbolised by the dotted “Data Link” line) as if it were one link.
If a standard regenerator is installed in a standard DSL connection as shown in FIG. 1, by default, any performance data received by the DLM Engine 16 (via the OSS management channel 14) will be in respect of link L1, and any new DLM profile will be applied in respect of link L1, since this is the link connected to DSLAM 12. More generally, it will be apparent that two scenarios exist:
(i) The regenerator may be installed without additional management/communication channels thereto; or
(ii) Additional management/communication channels may be made to the regenerator.
In scenario (i), the operator may (effectively) be blind to the additional link L2 (and any further links), making collection of performance data and diagnosis of faults thereon impractical. Further, the operator may be unable to reconfigure or control it (or them) individually at all, let alone in response to performance measurements in respect thereof as would be done in respect of the link L1 from the operator's DSLAM 12.
For scenario (ii), incorporating additional management/communication channels to the regenerator and suitable OSS interconnections to manage link L2 (and any further links) is possible, but this involves significant additional cost and complexity.
FIG. 2 illustrates the principal functional modules involved in the operation of a possible more complex DSL regenerator than the standard regenerator 10 of FIG. 1. The regenerator 20 of FIG. 2 is similar to that of FIG. 1 in that it is used on an ADSL connection between an exchange DSLAM 22 and a modem in CPE 28, with link L1 being connected to the regenerator 20 via a CPE chipset 202 and link L2 being connected to the regenerator 20 via a DSLAM chipset 206 such that the two links effectively convey user data along the whole connection (again symbolised by the dotted “Data Link” line) as if it were one link or V-LAN. An Ethernet Bridge 204 carries data received via one link L1/L2 (and demodulated by the modem in one chipset) to the other chipset for re-modulation and onward transmission over the other link L2/L1, such that the two links effectively convey user data along the whole of the connection (again symbolised by the dotted “Data Link” line) as if it were one link. In this case, however, an additional modem pair 25, 205 may be used to allow performance data to be collected by the operator from the regenerator. For this, a control module 208, which may hold pre-set configuration information for the regenerator, may also collect performance data from the chipsets and provide it to modem 205, which can send it over a management link LM via modem 25 and the OSS 24 to an operator-side Element Management System (EMS) 27. This separate management channel is symbolised by the dotted “Management Link” line.
A known regenerator, referred to as the “Digital ADSL Regenerator” (DAR) is discussed at http://www.densionbroadband.com/data/downloads/brochure_dar.pdf. This corresponds essentially to the device explained with reference to FIG. 2 above. This device connects up to four ADSL subscriber lines from an exchange, and uses an additional copper pair to connect a power unit to the device. This is said not only to provide power for the device but also to include a network management circuit, enabling supervision, monitoring and configuring of the equipment. It will be noted that there is no suggestion that any DLM processing is performed on the device, however, let alone that any information is provided to the device that may then be used in any such DLM processing.
Data concerning lines to end-user devices such as CPE devices can be collected by an operator and used for automatic configuration of such devices according to the CPE WAN Management Protocol (CWMP) or TR-069 protocol (Technical Report 069 of the Broadband Forum), which defines a bi-directional application layer protocol for remote management of end-user devices, allowing communication between Internet access devices such as modems, routers, gateways, set-top boxes, VoIP-phones, etc. and Auto Configuration Servers (ACS). It would therefore be foreseeable, in cases where standard regenerators are used, for an operator to collect data over the TR-69 protocol from the customer modem relating to the performance of customer-side links (such as links L2 in FIGS. 1 and 2), which could then be used by the operator's DLM system to select a profile to be applied to operator-side links (such as links L1 in FIGS. 1 and 2). TR-69 data collection is often unreliable, however. Further, this still does not allow for DLM processing to be done and for DLM profiles to be applied by or via the modem in the DSLAM chipset on a regenerator in respect of a link such as L2 (i.e. between a regenerator and a customer) in the manner that is done in respect of a link such as L1 from an operator-side modem.
Even if a sufficiently capable control module on a regenerator were to exist and be configured to cause the same profile to be applied in respect of the customer-side link as has been applied in respect of the operator-side link, while it may then be possible for an operator's DLM system to select the fastest profile that would stabilise both links and apply this to the operator-side link (i.e. indirectly causing that same profile to be applied by the regenerator in respect of the customer-side link), having the same profile for both links would generally result in lower performance levels than necessary, particularly on account of the likely disparity between the respective lengths, conditions, performance levels and capabilities of the individual links either side of the regenerator.
Referring briefly to prior art patent documents, US patent application US2006/0062209 (Riley) relates to methods for dynamic rate adaptation based on selective passive network monitoring. More specifically, it relates to a method for managing a session over a network that involves multiple end-points obtaining services via an application server, wherein, after the end-points have registered with the application server for the session, initial policies are established for network traffic flows for each end-point participating in the session; information is then determined about the network traffic flows for at least some of the end-points participating in the session; from the information determined about the network traffic flows, an identification is made as to which of the end-points is functioning as a host server for the session; then new policies are established for network traffic flows for the end-points, wherein under the new policies fewer network resources are reserved for each of the multiple end points other than and as compared to the end point functioning as the host server.
US application US2005/0169315 (Jiang) relates to systems and methods for accessing DSL data, and specifically to a method involving receiving a requested phone number corresponding to a DSL element; mapping the number to a port address for a DSLAM in communication with the (remotely-located) DSL element; sending an interrogation request to the port address of the DSLAM to interrogate the DSL element; collecting raw performance data of the DSL element; converting the raw performance data to analysed performance data; and displaying the analysed performance data.